Discovered in a forest near the Bosnian town Zavidovici, the ball has a radius of between four and five feet, and an "extremely high" iron content.

Dr Osmanagic believes the sphere proves the existence of an advanced lost civilisation dating back more than 1,500 years ago.

According to his fellow researcher Dr. Sam Osmanagich, the region used to have many more of the spheres well into the 20th century. Many were apparently destroyed in the 1970s due to rumours there was gold hidden in the middle of them.